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basic_json_view gains the read-only access functions of basic_json: operator[] and at() with keys and indices, front(), back(), find(), contains(), count(), begin()/end(), items() (with structured bindings from C++17 on), and type_name(). They throw the exceptions (ids and messages) that the const functions of basic_json throw; where basic_json has undefined behavior (operator[] with a missing key or an index out of range, front()/back() of an empty container), the view returns a discarded view or throws invalid_iterator.214. Objects are iterated in document order, and all members are visited. With duplicate keys, lookups find the first member, so that a lookup can stop at the first match; parse() keeps the last value. Keys of up to 16 bytes are compared with two overlapping loads instead of memcmp, and most keys are rejected by their length alone, from the index. The iterators and items live in detail/view/iterator.hpp, the lookups in detail/view/lookup.hpp. Tests compare every element and member of 2,000 generated documents with ordered_json, keys of every length around the load sizes, the exceptions against const basic_json, and the iterators. Signed-off-by: Niels Lohmann <mail@nlohmann.me>